The training of pilots for aircraft operation during emergency conditions has long been a concern for aircraft operators and pilot instructors. One particular type of training applies to pilots of multi-engine aircraft wherein the engines are mechanically linked so as to effectively provide a single, combined power output for propelling or lifting the aircraft.
One example of such aircraft is a dual engined helicopter wherein a pair of engines, linked by a gear box, together drive a main rotor for providing lift and maneuvering to the aircraft. Failure of one of the engines in such dual engine helicopters does not necessarily preclude operation of the aircraft with only the remaining operating engine, however the total available power is greatly reduced.
The powerplant in a modern helicopter is typically a gas turbine engine which usually operates within a normal rated power output range. Such engines are capable of producing power at a level significantly above the normal rated power range, however such operation in this elevated power output greatly reduces the lifetime of certain critical components such as the turbine blades, etc. Operation of a dual engine helicopter following the failure of one engine typically calls for the relaxing of normal engine control criteria and allows the aircraft operator to demand and receive power from the remaining operating engine at levels in excess of the normal operating range. The shift in control logic is justified in such emergency situations for obvious safety reasons.
The training of helicopter pilots for engine failure operation has long been a problem for instructors and aircraft operators. Realistic flight training with fully loaded aircraft requires the pilot to temporarily disable the fuel control on one engine, reducing it to an idle condition and hence effectively zero power output, and then operate the other engine within its elevated emergency rated power range. As noted above, such emergency power operation shortens the lifetime of the engine, increasing the frequency of expensive maintenance.
Aircraft gas turbine engines are rated by manufacturers and regulatory agencies for each permitted mode of operation. The rating of an engine establishes allowable time limits for operation at various power levels. Such limits may range from continuous at normal or part-throttle levels to under three minutes for the highest emergency power levels. One factor in determining a "one-time emergency" limited rating for an engine is the frequency with which the engine is expected to deliver such power. The training method discussed above requires repeated us of "emergency" power during training exercises, resulting in a lower power level than would be allowable for a truly one-time emergency use.
Another alternative commonly used within the industry is to reduce the weight of the aircraft to a minimum, operate the one engine at flight idle with the other engine being controlled within its normal rated operating range. This method, which attempts to give the trainee experience in operating the aircraft with reduced available power, does not accurately simulate the dynamics of the aircraft in a fully loaded condition. Such simulation is extremely valuable, particularly in practicing aircraft operation under windy, congested, or other complicating conditions.
One further disadvantage to the prior art methods described hereinabove results from operation of the helicopter with one engine in an idle condition. Should for any reason the power producing engine experience an unplanned failure requiring the idling engine to be brought up to a full power state, the aircraft will experience a period of time in which the total available power is extremely low thereby restricting maneuverability and possibly operating safety margins.
What is needed is a pilot training method and system which permits extended operation of the aircraft in a simulated, one engine failed mode and which does not significantly shorten the life of the aircraft engine components and which is able to accommodate an unplanned engine failure within the training mode without experiencing a severe, short-term cumulative power deficit.